System and method for controlling exposure format for an apparatus for exposing photographic film with image data

ABSTRACT

The present invention provides a control system for and method of controlling an apparatus of the type for exposing photographic film with image data which control system and method are adapted to compensate for variations in the exposure intensity, while also adjusting for different formats of image data. In one form, control system of the present invention determines the format of the image data, determines an exposure format in response to the format of the image data for producing an image on the film having a predetermined size, and calibrates an intensity for the exposure in response to the determined exposure format.

BACKGROUND OF THE INVENTION

1. Related Applications

The present application is related in subject matter to patentapplications filed simultaneously herewith of: Barry N. Stone, RichardC. Rice, John E. Lorbiecki and Stanley Berstein entitled APPARATUS ANDMETHOD FOR CONTROLLING FILM DENSITY FOR AN APPARATUS FOR EXPOSINGPHOTOGRAPHIC FILM WITH IMAGE DATA, now U.S. Pat. No. 5,021,978; andRichard C. Rice entitled CALIBRATION APPARATUS FOR A LIGHT SOURCE USEDFOR EXPOSING PHOTOGRAPHIC FILM WITH IMAGE DATA, now U.S. Pat. No.5,021,979, the contents of which are hereby incorporated by referenceherein.

FIELD OF THE INVENTION

The present invention generally relates to a method of and apparatus forexposing photographic film with image data and, in particular, to amethod of and apparatus for controlling the exposure format and theexposure intensity when exposing such photographic film with such imagedata.

2. Statement of the Prior Art

Photographic film has become the accepted archival medium for medicalimaging because of its high analog resolution and because of its longtime use with x-rays. Conversely, modern medical imaging techniques suchas computerized tomography, digital radiographic imaging, ultrasound andmagnetic resonance imaging have developed around the use of digitalimaging techniques where an image is made up of a great many pixels eachof which has an electronically represented brightness. In order to adaptthese new techniques to the accepted archival medium, apparatuses havebeen developed for creating a hard copy by "printing" the electronicimage data onto photographic film. These apparatuses are generallyreferred to as hard-copy cameras.

Thus far, the two primary approaches have used lasers and cathode raytubes as light sources to expose the film by illuminating each pixel tothe proper intensity. These devices have experienced some problems incontrolling the exposure or writing intensity and the resulting imagequality due to several inherently unstable factors. The problem isfurther compounded, if not made impractical, by trying to allow anyflexibility in the exposure format.

One attempt at controlling the various factors of exposure intensity isdescribed in U.S. Pat. No. 4,700,058. This patent teaches a generalscheme of using an exposure intensity calibrated to a predeterminedlevel for producing a gray scale on a film sample and then measuring thefilm density against a standard after developing the film. The measureddensities are then used to control an input amplifier, or a look-uptable in the digital version, to provide compensation for the responseindicated by the measured film densities. The exposure intensity isperiodically recalibrated using the same predetermined level, to adjustfor short term variations in light intensity.

Although this technique takes into account short term intensityvariations and film density variations, it does not allow for variationsof the input data format or compensate for its effect on exposureintensity.

It is desirable for a hard-copy camera to allow for variations in theimage exposure format. It is advantageous for the camera to be capableof accepting different formats of image data, such as images havingdifferent numbers of lines per image and different numbers of pixels perline. It is also desirable for a hard-copy camera to have the capabilityto prevent the appearance of raster lines between rows of image pixels.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a control system for andmethod of controlling an apparatus of the type which generates a beamfor exposing photographic film with image data. The control system andmethod are adapted to compensate for variations in the exposureintensity of the film, while also adjusting the operation of the controlsystem for different formats of image data. In one form, the presentinvention provides a control system for controlling an apparatus adaptedto expose photographic film with image data in accordance with anyone ofa multiplicity of possible image formats, each requiring a predeterminedexposure format, and comprises means for determining the image format ofthe image data, means for determining the exposure format in response tothe image format of the image data for producing an image on the filmhaving a predetermined size, and means responsive to the determinedexposure format for calibrating the exposure intensity.

In a refined version, the means for calibrating exposure intensityincludes means for producing an exposure test pattern in the determinedexposure format and adjusting the intensity of the exposure test patternto a predetermined intensity level. In another refinement the image datahas a multiplicity of possible formats of lines of pixels and the meansfor determining exposure format includes means for controlling thenumber of exposure or raster lines in the exposure format. This isfurther augmented by the means for controlling the number of exposurelines including means for causing the exposure of each pixel line ofimage data as a plurality of successive exposure lines and forcontrolling the line spacing thereof for causing overlapping betweensuccessive exposure lines.

In another form, a control system is provided for controlling anapparatus of the type for exposing photographic film with image datahaving a variable number of possible pixel lines of image data. Thecontrol system comprises means for determining the number of pixel linesof the image data for a particular image, and means responsive to thedetermined number of pixel lines of the image data for controlling thenumber of exposure lines and the spacing thereof used when exposing thefilm so that the resulting image produced on the film will be of apredetermined size.

The method of the present invention is used to control an apparatus ofthe type for exposing photographic film with image data having amultiplicity of possible image formats. The method comprises the stepsof (1) determining the image format of the image data for creating animage, (2) determining an exposure format as a function of the imageformat of the image data so as to produce the image on the film so thatthe image is of a predetermined size and (3) calibrating an intensityfor the exposure in response to the determined exposure format.

A BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustratively described with respect to theaccompanying drawings of which:

FIG. 1 is a system block diagram of one embodiment of the presentinvention;

FIG. 2 is a block diagram of a portion of the system of FIG. 1;

FIG. 3 is a block diagram of another portion of the system of FIG. 1;

FIG. 4 is a more detailed drawing of a portion of the embodiment of FIG.1; and

FIG. 5 is a side view of a portion of the embodiment of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 generally shows a system for producing hard copy film images fromdigitized image data. Generally included are a Control and Data Transfersection 12, an Image Data Processor section 14, a Printing section 16and a densitometer 17. The Control and Data section 12 would typicallyinclude a computerized control for the entire system 10 along with meansfor inputting, transferring and causing the printing of image data. TheImage Data Processor section 14 would typically include a frame memoryfor storing an image to be printed and some form of processor forhandling the data and converting it into proper form for printing. TheImage Data Processor section 14 is coupled to the control section 12 bymeans of a data bus 18 and an address bus 20 along with other knowncontrol lines, not shown. Printing section 16 would include the actualprinting mechanism including a source of light, an optical mechanism andthe film to be exposed. Also included would be the position andintensity controls for the light source. Printing section 16 is coupledto receive image data from the Image Data Processor section 14 via aseparate data bus 22. Densitometer 17 includes means for generating asignal responsive to the density or light transmittance of developedfilm.

FIG. 2 shows greater detail for the Control and Data Transfer section12. This section is constructed in the manner of a common microprocessorcontrolled computer and even uses a common Intel 80186 as themicroprocessor 24. Microprocessor 24 is coupled to other modules in thesystem via the data bus 18 and the address bus 20. A programmable readonly memory (PROM) 26 stores programmed instructions for themicroprocessor 24. A static random access memory (SRAM) 28, along with abattery backup 30, are used for the long term storage of data whichvaries during the system operation. A control interface 32 and controlpanel 34 allow for operator interface with the microprocessor 24, and aSCSI interface 36 provides communication with the cartridge disc drive38 to allow the inputting of image data into the entire processingsystem. Any suitable drive 38 may be used which has removeable disks toallow the transfer of image data from various imaging apparatuses to thepresent system. Lastly, a dual UART (universal a synchronous receivertransmitter) 39 provides two channels of serial communication for themicroprocessor 24.

FIG. 3 shows greater detail for the Image Data Processor 14. Asmentioned, a frame memory 40 is included which is coupled to the databus 18 at both its input 42 and its output 46 via a switch 44. Thisallows the inputting of data and the retrieval of data through the databus 18 for the purpose of testing the memory 40. The frame memory 40 isaddressed by a pair of counters 48 and 50 which are controlled by theaddress bus 20 and data bus 18, respectively. Counter 48 and 50 are both10 bit counters for addressing the rows and columns of memory 40,respectively, and are coupled thereto via a bus 52. Thus, in thisembodiment the memory 40 has a capacity of approximately one megabit by8 bits for storing an image as large as 1,024 by 1,024 pixels.

Image data is transferred from memory 40 in a pipelined manner. Theoutput 46 of memory 40 is coupled to an 8 bit register 54 for latchingimage data from memory 40 one pixel at a time. Image data is coupledfrom register 54 to the addressing input 55 of a look-up table 56.

Look-up table 56 has 256 addresses for the 8 bits of input data and 12bits of intensity data at each of the 256 addresses. This enablesexpansion of the intensity data from 8 to 12 bits and allows variousweighting to be applied to different ranges of the intensity data. Thisprovides implementation of gamma correction, a well known techniquewhich is typically implemented in analog form. This digitalimplementation is inherently more adjustable and stable. The look-uptable 56 may be addressed from the microprocessor 24 via the address bus20 and a switch 57, while data may be transferred to and from the table56 via the data bus 18 and switches 58 and 59.

The data output 60 of look-up table 56 is coupled to a 12 bit register62 to allow transfer of the data from the table 56. The 12 bit outputbus 22 is coupled to the register 62, a border intensity level memory 66and a blanking intensity level memory 68. By these means the entirespectrum of image data for each image may be transferred to the Printingsection 16 for exposure onto photographic film.

FIG. 4 shows further detail on the Printing section 16 which actuallyexposes the photographic film in accordance with the image datadelivered from the Image Data Processor 14. FIG. 4 representationallyshows the cathode ray tube (CRT) 80 which acts as a light source forexposing the film 82 along with an optical lens 84 and a shuttermechanism and motor 86. CRT 80 produces a beam of light 87 which isscanned over the film 82 to expose each pixel of an image. Film 82 isshown to be turned ninety degrees out from CRT 80 solely fordemonstrating a scanning pattern.

Further included in the exposure apparatus is a photo diode 88 which isused to measure the exposure intensity produced by the CRT 80 for thepurpose of ultimately controlling the photo density of the exposed film82. Photodiode 88 is set back somewhat from the surface 100 of CRT 80 inorder to receive light for more than just a small area of the surface.This is done to average the light of an area of the surface to preventadverse effects from any spot irregularities.

The image data is received from the 12 bit output data bus 22 of FIG. 3by a 12 bit digital to analog converter (DAC) 90. The output of DAC 90is an analog signal proportional to the intensity information containedin the digital image data. This analog signal is amplified by videoamplifier 92 and coupled through a buffer 94 to the cathode 96 of CRT80. In this manner, the digital image data is used to control theintensity of each pixel produced by the electron beam of CRT 80.

CRT 80 further includes a horizontal and vertical deflection yoke 98which controls the point at which the electron beam of CRT 80 impactsthe front surface 100 thereof and correspondingly where the light beam87 strikes the film 82. The control yoke 98 is coupled to and controlledby horizontal and vertical deflection control circuitry 102. Circuitry102 receives horizontal and vertical synchronization (sync) signals 104,106, respectively, from the microprocessor 24. They sync signals controlramp generators 108 and 110. These ramp generators are the primaryposition determining components for the electron beam of CRT 80. Theramp signals produced by generators 108 and 110 are coupled through adistortion and linearity correction circuit 112 which corrects for imagenonlinearity and the pin cushion effect caused at corners of the image.The resulting corrected horizontal and vertical drive signals arecoupled through amplifiers 114 and 116, respectively, to the coils ofyoke 98.

Photo diode 88 is connected through an amplifier 118 to a multiplexer120. In this manner photo diode 88 and other analog inputs may becoupled to an analog to digital converter (A/D) 122 which producesdigital signals for coupling through the data bus 18 to microprocessor24. Converter 122 is of the type which either averages or integrates theinput signal over a predetermined period of time. One such converterwhich performs this function is a dual-slope converter. The period oftime is typically one line cycle of the power supply (i.e. 60 Hz.). Thiscauses the averaging out of any supply based interference.

FIG. 5 shows a side view of greater detail of the densitometer 17 ofFIG. 1. Although referred to as a densitometer, the member 17 is notrequired to measure density against any standard. The densitometer meansrequired for the present embodiment merely needs to be sufficient togenerate an electrical signal which is responsive to the relativedensity or transmittance of different portions of developed film. Forthis purpose, a member 123 is shown which has a centrally located slot124 for receiving a piece of developed film 125. Member 123 alsoincludes a channel 126 which intersects slot 124 and is locatedgenerally orthogonally with respect thereto. Affixed within channel 126and on separate sides of slot 124 are a light which intersects slot 124and is located emitting diode LED 127 and a photodiode 128. The LED 127is powered by a regulated power supply, not shown, to provide a lightsource having short term stability sufficient for the measurement periodof the present embodiment.

A stepper motor, not shown, is used to move the member 123 orthogonallywith respect to the plane of the drawing and along a portion of the film125. The stepper motor is controlled via appropriate drive circuitry bythe microprocessor 24.

THEORY OF OPERATION

As mentioned, the entire apparatus is controlled by microprocessor 24 inaccordance with program instructions stored in PROM 26. These programinstructions are set forth generally in Table 1 which is described ingreater detail below.

In general, the first step of the printing process generally includes afilm transmittance test upon which calibration of the exposure orwriting intensity is based. The transmittance test determines relativestandard black and white film densities or transmittance in accordancewith industry standards, as a factor of the base plus fog transmittanceof the actual film being used. This allows monitoring of the developingprocess to compensate for variations in film response and chemical usageand age. The transmittance test is typically performed at the beginningof each day and at the start of each new package of film. It may also beperformed at any time at the option of the operator. Thusly, any suspectconditions may be tested for and compensated for throughout the printingprocess.

The transmittance test is performed by exposing a piece of film with apair of gray scales centered around approximated standard black andwhite exposure intensity levels. Also included is a substantially clearportion of the film. The writing intensity of each gray scale step isknown. These intensities may be factory set or stored in the static RAM28 from a previously run transmittance test.

After the film is developed, it is placed in the densitometer 17. Atransmittance signal is generated therein which is responsive to therelative densities or transmittance of the gray scale steps, includingthe clear portion. The microprocessor 24 then takes the signal levelrepresenting the clear portion and calculates transmittance signallevels representing relative standard black and white film densitiesbased upon the clear film portion. Based upon the calculated standardtransmittance signal levels, the transmittance signal for the gray scalesteps and the known exposure intensities used to produce the gray scalesteps, it is possible for microprocessor 24 to determine the exposureintensities that are necessary to produce each of the standarddensities. These intensities are referred to as the standard black andwhite exposure intensities. They may be determined by any suitablemethod.

Each standard exposure intensity may be interpolated from the twoexposure intensities corresponding to the transmittance signal levelmeasured on either side of the calculated standard transmittance signallevel. It may alternatively be desirable to perform a second exposureprocedure in order to more accurately determine the standard exposureintensities. This would be done using a smaller overall range ofexposure intensities around each of the values determined from the firstexposure procedure. The range may even be defined by using the measuredfilm transmittances and their respective exposure intensities, whichbracket each of the calculated standard transmittance signal levels, asthe minimum and maximum levels for the second set of gray scales whichare exposed on a second piece of film. The results developed from thesecond exposure may then be used to interpolate more accurate exposureintensities for the calculated standard black and white film densities.Using the second exposure process eliminates nonlinearities which woulddegrade the accuracy of interpolation after the first exposure process.

It is also possible to base the first exposure process on a narrowerrange of exposure intensities. However, this may require repetition ofthe exposure if the calculated standard transmittance signal levels areoutside of either or both of the gray scale transmittance signal rangesproduced.

Once again, the end result of the film transmittance test is thedetermination of standard exposure intensity levels which may bemeasured by photodiode 88 so that the intensity output of CRT 80 may beaccurately calibrated.

Once the standard exposure intensities for black and white aredetermined, the apparatus is ready for use in the printing process. Theoperator typically inserts a disk cartridge into the disk drive 38,which disk cartridge includes image data to be printed. The image datamay be recorded on the disk by any suitable means. Imaging apparatusesmay be adapted to record the image data onto disks.

The image data may have any one of a wide variety of formats ofhorizontal lines of image pixels. That is, the images may have any givennumber of pixel lines and any given number of pixels per line. Theparticular pixel format of the image data is noted in a header block onthe cartridge disk so that microprocessor 24 may read the header blockand determine how many images are on the disk, what the pixel format ofthose images is and where those images are located on the disk. The diskmay also be used to carry gamma correction information from theparticular instrument which produced the images. Because of theflexibility of the pixel formatting of the images, this system mayaccept disks from a variety of different types of imaging instruments.Such different instruments may require different gamma correctionschemes for either linearizing or enhancing various ranges of intensity.

Once the microprocessor 24 has determined the pixel format of the imagerepresented by the stored image data it can then calculate the exposureformat which it will use to reproduce the image on film. This initialexposure format determination is made simply with respect to the numberof horizontal pixel lines located in the vertical direction on theimage. This is done for purposes of calibrating the CRT intensity levelsthrough the setting of the intensity values of look-up table 56. Theformatting of the number of pixels per line does not affect exposureintensity and thus is not determined at this point.

The present embodiment prints each horizontal pixel line of image dataas a plurality of overlapping exposure or raster 7 lines 85 each ofwhich is separately produced by the light beam 87. The number ofsuccessive exposure lines and the spacing of all of the exposure linesover the image is varied depending upon the pixel format of the imagerepresented by the image data on the disk and the desired exposureformat or final print size on the film 82. This variability allows thepresent invention to accept images having different image data formats.

For example, images typically have between 400 and 1000 horizontal pixellines. For formats having up to approximately 500 pixel lines, thenumber of successive exposure lines per image or pixel line of datawould be 4. For 500 to 700 pixel lines, the repetition would be 3, andfor 700 to 1000 pixel lines, the repetition would be 2. The amount ofoverlap between successive exposure lines depends on the spot size orline width and the spacing of the exposure lines. It is preferred thatthe spacing be less than the spot size or line width in order to causeoverlapping. It should be noted that successive image or pixel lines areallowed to overlap to remove the appearance of a raster scan.

In the actual exposure process, the number and the spacing of thehorizontal lines is controlled by the horizontal sync signal on line 104from microprocessor 24. The vertical ramp generator 110 operatesconstantly while the horizontal sync signals are controllably delayed toprovide a controllable spacing for successive exposure lines. Becausethe CRT scan rate is arbitrarily set by the present embodiment and isnot run at the normal high video presentation rate of 30 frames persecond, great flexibility is available for the timing control of thehorizontal sync signals.

As mentioned, once microprocessor 24 determines the image format of theimage represented by the image data on the disk cartridge, it determinesthe repetition rate and line spacing for the actual printing process.Microprocessor 24 then takes this spacing and produces separate blackand white test patterns on the CRT 80, which patterns are sensed by thephotodiode 88 for intensity level and adjusted until the so measuredintensity levels match the standard exposure intensity levels determinedfrom the film transmittance test.

The method of adjustment used may be described as successiveapproximation. The twelve bits of input data for DAC 90 are controlledby microprocessor 24 which sets the contents of register 62. Each of thetwelve bits, which are originally set high, is sequentially switched lowproceeding from the most to the least significant bit. After eachswitching, the photodiode 88 is tested to see if its output, as measuredby A/D 122, is either above or below the stored standard intensityvalue. If photodiode 88 indicates a low reading, then ext sequential bitis switched. If the indication is high, the bit just switched is resethigh and then the next sequential bit is switched low. When the processis completed the intensity level measured by photodiode 88 is the sameas that stored for the particular standard intensity value being set.

When the CRT output is adjusted to produce the same intensity values asthose stored for the standard intensities, the digital signals appliedto DAC 90 for producing each of these signals are then stored in look-uptable 56 along with gray scale intermediate data as determined bymicroprocessor 24. This gray scale data may be linear or nonlinear andmay implement a gamma correction function.

The next step in the printing process includes determining thehorizontal output rate for the frame memory 40. This horizontal outputrate is varied in order to allow image data of whatever size to fit inthe desired size of the final image as printed. The adjustment is madeby simply varying the horizontal pixel output rate from frame memory 40.Each pixel on a horizontal line of the image is held at the output 46 offrame memory 40 for a controllable number of system clock pulses,depending upon the determined printing or image format. Each horizontalpixel may be held at the output for the same amount of time, or theamount of time may be varied between each pixel so that an image dataformat of a given number of pixels will fit the fixed output image size,or exposure format, using a fixed microprocessor clock rate. Forexample, horizontal pixels may be alternately outputted for six andseven clock pulses across the entire width of the image in order tocause a proper fit of the given image data format within the fixedexposure format. The same output clock pulsing is repeated for eachhorizontal line with the result of no noticeable distortion to theprinted image.

Once the vertical repetition and overlap rate and the horizontal pixeloutput rate are determined, an image is transferred to the frame memory40 and printed. Subsequent images on the same image data disk areprinted using the same exposure format settings. If images having adifferent data format are to be printed, the DAC values for look-uptable 56 must be reset to produce the standard exposure intensity valuesfor the new format. If the package of film, or any other densitysensitive factor, changes, the film transmittance test will be rerun toproduce new standard black and white exposure intensities. Also, the DACvalues of look-up table 56 will be reset. The above process iscontrolled by microprocessor 24 in accordance with program instructionstored in PROM 26. These program instructions are represented in thesteps set forth in Table 1.

TABLE 1 PROGRAM STEPS

130 Initialization

132 Film transmittance Test

134 Intensity Calibration

136 Find black reference intensity spread

138 Find white reference intensity spread

140 Calibrate 19 intensities for 1024 ppl+512 1pf

142 Expose gray scales

144 Measure developed film transmittance

146 Cal. ref. black and white transmittance signal levels

148 Approx. reference intensities and determine fine range

150 Determine new intensity readings

152 Intensity Calibrate fine range

154 Expose gray scales

156 Measure fine gray scale transmittance

158 Interpolate black and white intensity levels

160 Determine image format

162 Determine exposure format

164 Calibrate black and white intensities

166 Find white dac valve

168 Find black dac valve

170 Fill in Look-up Table

172 Determine pixel clock rate

174 Image data to memory 40

176 Print Image

More specifically, when the apparatus is first turned on, themicroprocessor 24 goes through a common initialization sequence 130. Atthis point, all of the system components which may be tested by themicroprocessor 24, including itself, can be so tested. Microprocessor 24is then ready to control the apparatus to perform its intendedfunctions.

After the initialization step 130, the operator typically initiates afilm transmittance test 132 which includes several program substeps134-158. The first general step of a film transmittance test is referredto as the Intensity Calibration step 134 which calibrates the CRTintensity for a gradation or gray scale of intensity levels around eachof a pair of approximated standard black and white exposure intensitylevels. Step 136 takes the desired approximated intensity reading forthe black reference and determines a spread of intensity readingstherabout. Step 138 takes the approximated white intensity reading anddetermines a spread of white intensities beginning with base plus fog.Step 140 performs the actual calibration process for the CRT intensityfor 19 different intensity levels, 10 around the black reference and 9plus a clear density portion around the white reference, all based upona exposure format of 1024 pixels per line (ppl) and 512 lines per frame(1pf). The density of the clear portion is commonly referred to as baseplus fog. The calibration process is performed by the same successiveapproximation technique as is described above. It is performed for eachof the 19 gray scale steps around the black and white reference values.

Once the 19 exposure intensity levels are calibrated, step 142 exposes apiece of film with a pair of gray scales around each of the black andwhite standard intensities. This exposure is done as two separate steps,one for each of the black and white gray scale patterns.

Once the film is exposed, the operator removes it from the instrumentand passes it through the developing process. After developing, the filmis placed in the densitometer 17 and step 144 measures the relativedensity or transmittance between each of the 19 gray scale portions inaddition to the base plus fog area. This is accomplished by generating atransmittance signal which is responsive to the various densities on thefilm. The stepper motor is used to move the member 123 past each of thegray scale steps while the transmittance signal is read from photodiode128 and converted to a digital value by A/D 122.

With the base plus fog transmittance signal level, program step 146 canthen calculate the transmittance signal levels that correspond tostandard black and white densities which have been standardized by theindustry as a percentage of the base plus fog reading for the film. Oncethe black and white transmittance signal level calculations are made, acomparison is made by step 148 against the 19 gray scale relativetransmittance measurements to determine which two transmittance signallevels bracket each of the calculated standard transmittance signallevels.

At this point it is possible to either interpolate the necessaryexposure intensity levels for producing the calculated transmittance orto perform another exposure step to further refine the measurement.Because the exposure process is nonlinear it is preferable to performanother gray scale exposure process to get closer to the actualtransmittance readings and thereby minimize inaccuracies from a linearinterpolation process. For this purpose, step 150 approximates thereference intensities and determines a new set of intensity readings forgray scales located around the approximated intensities. Step 152 thencalibrates this fine range of intensity values as in step 134. Theoperator then inserts another piece of film and step 154 again exposes apair of gray scales intended to narrowly bracket the calculated blackand white transmittance signal levels. After this piece of film isdeveloped it is inserted into the densitometer 17 which is controlled bystep 156 to measure the fine gray scale transmittance values. Themicroprocessor 24 again has available to it, calibrated and measuredintensity levels which produced measured film transmittance signallevels. It uses the measured levels in comparison with the calculatedblack and white film transmittance signal levels of step 146 todetermine the intensity levels at which it should calibrate CRT 80 toproduce the calculated standard black and white transmittance levels.Step 148 thereby interpolates the black and white intensity levels basedupon the calculated black and white film transmittance signal levels todetermine the standard black and white exposure intensities.

Once the film transmittance and the standard exposure intensities havebeen determined, the software examines the image format information andcalibrates the exposure intensity. For this purpose, step 160 causes themicroprocessor 24 to look at the cartridge disk drive and determine theformat of the images stored thereon. This is done solely with respect tothe number of lines per frame indicated on the cartridge disk drive.Step 162 then determines the exposure format, the number of successiveexposure lines per image line and the spacing thereof. With the verticalexposure format determined, step 164 can then proceed with calibratingthe black and white intensity levels.

Step 166 causes a test pattern to be generated on CRT 80 which is sensedby photodiode 88. The signal therefrom is converted by A/D 122 and fedto microprocessor 24 where it is compared against the stored white,reference exposure intensity reading. During this comparison, the mostthrough least significant bits of register 62 are successivelyapproximated until the converted reading from photodiode 88 matches thewhite reference exposure intensity. Step 168 likewise repeats thisprocess in comparison with the black reference exposure intensity.

Step 170 takes the twelve bit DAC values determined to produce thereference exposure intensities and load them into look-up table 56 asthe black and white DAC values. Microprocessor 24 then calculates orotherwise determines intermediate DAC values and likewise loads theminto table 56.

Step 172 again checks the image data format and determines thehorizontal pixel output rate for frame memory 40. Step 174 then loads aframe of image data from the disk into frame memory 40. Lastly, step 174causes the image data to be appropriately clocked out of memory 40 toDAC 90 while the horizontal and vertical sync signals 104, 106 controlthe location of the CRT beam and the image is printed.

The above embodiments are intended to be taken in an illustrative andnot a limiting sense. Various modifications and changes may be made tothese embodiments by persons skilled in the art without departing fromthe present invention as defined in the appended claims. Suchmodifications may include the use of analog instead of digitized imagedata.

CONCLUSION

As described, the present invention provides a hard copy camera with ameans for accurately controlling the image format while compensating forvariations in exposure intensity. This approach allows image data fromdifferent sources to be printed using the same camera. For example,where a hospital might have both different types of ultrasonic imagingequipment (cardiac versus abdominal) and ultrasonic imaging equipmentfrom different manufacturers, it is now possible for the apparatus ofthe present invention to be used to produce hard copy images for all ofthe different apparatuses. In the past it was necessary to have separatehard copy cameras for each different type and make of instrument greatlyelevating the cost of such instrumentation.

The exposure method of the present invention enables an exposurescanning rate which is much lower than normal video scanning rates. Thisallows very accurate control of the exposure format and the printedimage including control over the appearance of raster lines. The slowerscan rates also allow the use of twelve bit resolution for the exposureintensity values. Twelve bit DACs are currently not available for use atnormal video conversion rates. Lastly, the slower scan rates also allowthe use of less expensive components than are required by normal videorates.

The exposure method which includes the repetition of lines for thepurpose of enlarging the image is more accurate and less expensive thanthe image processing and interpolation methods which are commonly used.

The present invention specifically allows adjustment and calibration ofthe writing intensity based upon the exposure format, once that isdetermined. Both the exposure format selection and the resultingexposure intensity calibration are provided automatically by the aboveembodiment, reducing operator training requirements.

What is claimed is:
 1. A system for controlling an apparatus of the typefor exposing photographic film with image data in any one of a pluralityof different imaging formats, each of said formats being defined by aunique pixel array comprising a predetermined number of lines and apredetermined number of pixels per line which serve to reconstruct animage represented by said image data, said system comprising:means fordetermining the imaging format of a particular set of image data,including the number of lines and the number of pixels per line of saidformat; means for determining an exposure format defining the manner inwhich the film is exposed in response to the determined imaging formatfor the image data so as to produce an image of predetermined size onthe film; and means, responsive to the determined exposure format, forcalibrating the exposure intensity created by the apparatus whenexposing the film in accordance with the determined exposure format. 2.The control system of claim 1, wherein the means for calibrating theexposure intensity include means for producing an exposure test patternin the determined exposure format and adjusting the exposure intensityproduced in the exposure test pattern to a predetermined exposureintensity level.
 3. The control system of claim 1, wherein the means fordetermining the exposure format includes means for controlling thenumber of raster lines in the exposure format, as a function of thenumber of lines of said determined imaging format.
 4. The control systemof claim 3, wherein the means for controlling the number of raster linesincludes means for generating the raster line as a plurality ofsuccessive overlapping exposure lines on said film.
 5. The controlsystem of claim 1, wherein the means for determining the imaging formatof the image data includes means for determining the number of pixelsper line, and the means for determining the exposure format includemeans, responsive to the determined number of pixels per line, forcontrolling the width of each pixel along its respective line forproducing a predetermined line length on the film.
 6. The control systemof claim 5, wherein the apparatus includes memory means for storing thepixel data, means for generating said pixel data to the output of saidmemory means at a variable rate, and further wherein the means forcontrolling pixel width is responsive to the output rate of the pixeldata from the memory means and controls the pixel width as a function ofthe output rate.
 7. The control system of claim 6, wherein the means forcontrolling pixel width includes means for changing the output rate fromthe memory means between each pixel.
 8. A control system for controllingan apparatus of the type for exposing photographic film to an imagerepresented by image data and having any one of a variable number ofpossible lines and a variable number of pixels per line of image data,said control system comprising:means for determining the number of linesand the number of pixels in each line of the image data representingsaid image; and control means, responsive to the determined number oflines and number of pixels in each line of the image data forcontrolling the number of exposure lines and the spacing thereof whenexposing the film with said apparatus.
 9. The control system of claim 8,wherein the control means includes means for exposing the film with eachline of image data as a plurality of successive exposure lines with eachsuccessive exposure line partially overlapping the previous exposureline.
 10. The control system of claim 9, wherein the apparatus includesa light source for producing a light beam and for exposing the film bysuccessively sweeping the light beam over the film to produce thesuccessive exposure lines, and further wherein the control meansincludes sweep circuit means for changing the relative position betweenthe light beam and the film in a direction on the film which issubstantially orthogonal to the lines of image data and at a constantrate, and means for controlling the spacing of successive exposure linesby controlling the amount of delay between the exposure by the lightbeam of each successive exposure line on the film.
 11. The controlsystem of claim 8, further comprising means for calibrating theintensity of the exposure to a predetermined intensity level in responseto the number of pixels in each line and the spacing thereof used forexposing the film.
 12. A method of controlling an apparatus of the typefor exposing photographic film with image data having any one of aplurality of possible image formats each defined by a predeterminednumber of lines and a predetermined number of pixels per line of imagedata, said method comprising the steps of:determining the image format,including the number of lines and the number of pixels per line, of aset of image data; determining the exposure format in response to theimage format of the image data for producing an image of a predeterminedsize on the film; and calibrating the exposure intensity provided by theapparatus in response to the determined exposure format.
 13. The methodof claim 12, wherein the step of calibrating an exposure intensityincludes producing an exposure test pattern in the determined exposureformat and adjusting the exposure intensity of the exposure test patternto a predetermined intensity level associated with said exposure format.14. The method of claim 12, wherein the step of determining an exposureformat includes controlling the number of exposure lines and pixels inthe exposure format.
 15. The method of claim 14, wherein the step ofcontrolling the number of exposure lines and pixels includes exposingeach line of image data as a plurality of successive exposure lines andcontrolling line spacing thereof for causing overlapping betweensuccessive exposure lines.
 16. A control system for use in controllingan apparatus of the type for exposing photographic film to an image inany one of a plurality of pixel array formats and represented as a setof image data, said control system comprising:means for sending saidimage data and for determining the pixel array format of the imagerepresented by said image data; and control means, responsive to thedetermined pixel array format, for controlling the height and width ofeach pixel of said array when exposing the film with said apparatus soas to produce an image on said film.
 17. The control system of claim 1,wherein the means for determining the exposure format includes means,responsive to the predetermined number of pixels per line of said pixelarray, for controlling the width of each pixel along its respective lineso as to produce a predetermined line length on the film when exposingthe film in accordance with the determined exposure format.